I have a son who is physically much, much smaller than his classmates. I will be honest with you and tell you that it has never held him back. He is the smallest guy on his soccer team - but he is also the hardest working. He looks the youngest in many situations - but he gets the job done. People only misjudge him once - and then they get to know him.
You need to do some serious self-reflection and find a way to turn around your approach to life.
I wish you the best.